This invention relates generally to methods and apparatus for diagnosing intermittent electrical circuits, and more particularly to methods and apparatus for diagnosing intermittent communications in electrical circuits using brushes and sliprings, including circuits used CT scanning systems using sliprings to send information between stationary and rotating sides of a gantry.
In at least one known computed tomography (CT) imaging system configuration, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system and generally referred to as the xe2x80x9cimaging planexe2x80x9d. The x-ray beam passes through the object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is dependent upon the attenuation of the x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile.
In known third generation CT systems, the x-ray source and the detector array are rotated with a gantry within the imaging plane and around the object to be imaged so that the angle at which the x-ray beam intersects the object constantly changes. A group of x-ray attenuation measurements, i.e., projection data, from the detector array at one gantry angle is referred to as a xe2x80x9cviewxe2x80x9d. A xe2x80x9cscanxe2x80x9d of the object comprises a set of views made at different gantry angles, or view angles, during one revolution of the x-ray source and detector. In an axial scan, the projection data is processed to construct an image that corresponds to a two dimensional slice taken through the object. One method for reconstructing an image from a set of projection data is referred to in the art as the filtered back projection technique. This process converts the attenuation measurements from a scan into integers called xe2x80x9cCT numbersxe2x80x9d or xe2x80x9cHounsfield unitsxe2x80x9d, which are used to control the brightness of a corresponding pixel on a cathode ray tube display.
Data and instructions are communicated bidirectionally between electronics on stationary and rotating sides of the gantry. For example, communication is sent across a copper band on a slipring. A brush block maintains an electrical connection to the copper band. A problem with known systems of this type is that there is no indication of whether a connection is broken or whether the connection is simply inactive, with no data being sent. Moreover, sliprings also are known to have problems with xe2x80x9cmicro disconnects,xe2x80x9d in which a brush temporarily loses electrical contact from the slipring.
It would therefore be desirable to provide methods and apparatus to monitor the state of brush contacts while a system, such as a CT imaging system, is in operation, and to provide a diagnosis of disconnection events that occur.
There is therefore provided, in one embodiment of the present invention a method for detecting interruptions of continuity in a circuit, including steps of transmitting a signal through a brush contacting a conductive band of a slipring, the brush and slipring having a relative motion; determining whether parameters of the signal transmitted through the brush and the slipring are indicative of a circuit interruption; and providing an indication of an interruption when the parameters of the signal transmitted through the brush and slipring are indicative of a circuit interruption.
This embodiment provides a method for monitoring the state of brush contacts within a system, such as a CT imaging system, while it is in operation. In addition, information provided by this method embodiment can be used to localize and diagnose disconnections when they occur.